1. Technical Field
This disclosure relates to sigma-delta modulators, to analog-to-digital converters having a sigma-delta modulator, and to methods of converting a signal.
2. Description of the Related Art
Sigma-delta (ΣΔ) modulators are employed in analog-to-digital converters (ADCs). U.S. Pat. No. 6,404,368 discloses in FIG. 3 and its accompanying text a ΣΔ modulator to be used in an over-sampling type ADC, which includes an analog ΣΔ modulator coupled to a digital ΣΔ modulator. The analog ΣΔ modulator includes a digital-to-analog converter (DAC) which converts a one-bit feed-back signal to an analog signal, an analog adder or subtractor which calculates a difference between an output signal transmitted from the DAC and an analog input signal. The analog ΣΔ modulator also has an analog integrator, which integrates output signals transmitted from the analog adder or subtractor, and a first quantizer which converts an output signal transmitted from the analog integrator, into a digital signal. The digital ΣΔ modulator includes a digital adder or subtractor which calculates a difference between an output signal transmitted from the first quantizer and the one-bit feed-back signal, a digital integrator which integrates output signals transmitted from the digital adder or subtractor, a second quantizer which converts an output signal transmitted from the digital integrator into a one-bit digital signal, and a delay element which delays the one-bit digital signal transmitted from the second quantizer and feeds the thus delayed signal back as the one-bit feed-back signal. Since the feedback signal transmitted to the analog modulator is a one-bit signal, distortion caused by non-linearity error of the DAC can be reduced.